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5.4Mineral Groups
Objectives
1) Describe the properties of the most common minerals (silicates and
carbonates).
2) Describe tests used to identify mineral groups.
Major Silicates
 90+% of the minerals in
Earth’s crust are members
of the silicate family
 Silicate: a compound of
silicon, oxygen, and usually
one or more metallic
elements
 Basic building block is the
silica tetrahedron
 Classified by the ways the
tetrahedra are linked
together
Quartz
 Second most abundant
mineral in the Earth’s crust
 Made entirely of tightly
bound silica tetrahedra
 Chemical name: silicon
dioxide
 2 oxygen atoms per silicon
atom
Quartz cont’d
 Looks:



Glassy or greasy luster
Pure quartz = colorless or
white
Other colors = rose,
amethyst (purple), smoky
 Fracture:

Conchoidal or irregular
 Hardness:

7 on the Mohs scale
 Common property used
to identify it
 Hardest of the common
minerals
Quartz cont’d
 Hardness and how it looks:
 Make it ideal for certain
uses
 Watch movements
 Prisms
 Heat lamps
 Lenses
 Glass
 Paints
 Jewelry
Quartz cont’d
 Found in granite
 Important part of many
other types of rocks
 Most sands are made
mainly of quartz
Feldspars

Makes up 60% of Earth’s crust

Share 3 features




2 directions of cleavage
Hardness of 6
Pearly luster
Made of aluminum, oxygen, and
silicon atoms


Creates a net electrical charge
Balanced by the addition of
other metals
 Potassium
 Sodium
 calcium
Feldspars cont’d
 2 major groups
 Potassium feldspars
 Most common is
orthoclase
 Light-colored pink
or salmon
 2 cleavage surfaces
meet at right angles
 Most commonly
found in granite
Feldspars cont’d
 Sodium-calcium feldspars
 Plagioclase
 Albite and
labradorite
 Range in color from
white to gray
 2 cleavage surfaces
meet at slightly less
than a right angle
 One cleavage
surface is often
marked by fine
parallel lines
(striations)
Feldspars cont’d
 Important rock-forming
minerals
 Important economically
 Manufacture of glass and
ceramics
Other Silicates
 Pyroxene family
 Occur widely
 Cleavage surfaces meet at
nearly right angles
 Common member
 augite
Other silicates cont’d
 Ferromagnesian silicate
 Can belong to almost any
of the silicate families
 All contain iron and
magnesium
 Always dark in color
 Example
 Augite
 2 good cleavages
 Hardness 5-6
Other Silicates cont’d

Mica family





Soft
 Hardness = 2.5
Perfect cleavage
 Form flat crystals that cleave
in only one direction
 Makes thin sheets or
flakes
Can be easily picked out of
rocks
Examples
 Muscovite (white mica)
 Silvery white
 Biotite
 Dark brown or black
Used for paints, plastics, rubber,
roofing, electronic insulators
Carbonates
 Carbonate: a mineral made
of negatively charged
carbonate ions bonded to
positive metal ions
 1 carbon atom covalently
bonded to 3 oxygen atoms
 Examples
 Limestone
 Marble
Carbonates cont’d

More examples


Calcite (calcium carbonate)
 Most common carbonate
mineral
 Colorless or white
 Hardness = 3
 Can be scratched with a
knife
 Bubbles with the acid test
Dolomite (calcium magnesium
carbonate)
 Occurs as coarse or fine grains
in dolomitic limestones
 Hardness = 3.5-4
 Cannot be scratched with
a knife
 Will not react during an acid
test
Oxides and Sulfides
 Contain significant
amounts of iron
 Not as common as silicates
or carbonates
 Used to make steel,
magnets, car parts,
medicines, cosmetics,
plastics, and paints
Oxides and Sulfides
 Oxide: a mineral made of a
metal element combined
with oxygen
 Sulfide: a mineral made of
a metal element combined
with sulfur
Hematite
 Most common iron oxide
 Usually red
 Earthy luster
 Uneven fracture
 Some have a silvery
metallic luster
 Gemstones
 Leave a red-brown streak
on a streak plat
Magnetite
 Black iron oxide
 Attracted to magnets
 Example
 Lodestone
 Natural magnet
 First compass needles
Pyrite
 Iron sulfide
 Most common sulfide
mineral
 Color
 Pale brass to golden yellow
 Commonly referred to
fool’s gold
5.4 Exit Ticket
1) Describe the properties of
the most common minerals
(silicates and carbonates).
2) Describe tests used to
identify mineral groups.